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\footnotesize
\psaxes[arrows=<->,ticks=none,labels=none](0,0)(-0.5,-0.5)(3.5,2.5)
\psplot[linecolor=blue]{0.5}{3.1}{2-(x-1.8)^2}
\psline[linecolor=red,linestyle=dashed](1.8,0)(1.8,2)(0,2)
\psline[linecolor=red,linestyle=dashed](1,0)(1,1.36)(0,1.36)
\psxTick(1.8){x_0}
\psxTick(1){x}
\psxTick(0.5){x_0-\delta}
\psxTick(3.1){x_0+\delta}
\psyTick(2){f(x_0)}
\psyTick(1.36){f(x)}
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